The invention concerns the field of timepiece mechanisms, and more specifically the field of escapement mechanisms.
In a mechanism of this type, the escapement lever cooperates both with a balance and with an escapement wheel. On both sides, the escapement lever works with shocks, on the one hand via the fork, including horns, which cooperates with the impulse pin of the balance and on the other hand via the pallet stones which cooperate periodically with the escapement wheel. These incessant shocks generate wear, and thus over time cause deterioration of the properties of the movement. In particular, in an escapement mechanism, wear at the fork notches results in a decrease in the overall efficiency of the escapement and a drop in amplitude. The problem is therefore to reduce the wear of the escapement mechanism, particularly the escapement lever, and to make the contact zone between the escapement lever and the balance elastic, while respecting the space requirements imposed by the mechanism.
Few patent documents mention the problem of wear. The rare solutions put forward propose surface coatings, a particular choice of materials, the use of bearings, or reducing inertia by using short lever arms. The choice of particular materials or surface coatings does not reduce shocks, but delays the effect thereof. The use of ball bearings is ill-suited to a system permanently subject to shocks, and the lifetime of bearings in such mechanisms is generally reduced, which is incompatible with a timepiece. Reducing inertia is more advantageous, but it is difficult to act on an existing movement and modify its kinematics.
It will be noted in this regard that another method of reducing inertia is known from EP Patent No. 0 732 635 in the name of CSEM, through the use of silicon or similar components.
Some patent documents concern mechanical resistance, which is the closest problem to that addressed by the invention.
Thus, there is known U.S. Pat. No. 2,717,488 in the name of La Générale Horlogère relating to an escapement with a reduced noise level, which includes an escapement wheel with radial notches for damping shocks associated with the impact of the escapement wheel teeth on the pallet-stones, wherein each tooth is also able to rest on the next tooth, because of the flexibility provided by the notch, which confers a certain robustness on the wheel in addition to the desired flexibility. The notches must be sufficiently large to grant the whole of each tooth flexibility relative to an attachment area in relation to which the notch allows each tooth a degree of freedom to pivot. This arrangement is not applicable to numerous components, for which pivoting mobility is incompatible with their operational kinematics.
There is also known EP Patent No. 1 870 784 in the name of OMEGA, which discloses a wheel without a felloe but including teeth, and which proposes a solution preventing the teeth from being damaged by shocks. The wheel according to that patent includes flexible bent arms, which bend tangentially and with decreasing width towards the wheel periphery. These arms each include an end tooth, which is also flexible. Although this type of wheel may suit an escapement wheel, like the preceding patent document, the arrangement thereof is less suitable for the particular kinematics linked to certain components such as escapement levers. Moreover, fitting an escapement mechanism with this type of escapement wheel involves replacing the original wheel with this special wheel, without any possibility of re-using the original one.
Various documents propose mechanisms intended to reduce the operational play in the gears, or even to reduce the effect of impact or impulses on some components. Thus there is also known EP Patent Application 1 555 584 A1 in the name of ROLEX SA, which discloses a toothed wheel set, with teeth for taking up play, including slots arranged in the teeth, which are combined with stop means for limiting the amplitude of movement allowed by the slots in accordance with the gear play to be taken up. In a similar manner, JP Patent Application No. 63 130961 in the name of KIYOUIKU HAGURAMA KOGYO KK discloses teeth whose elasticity is provided by slots or chambers. EP Patent Application No. 1 380 772 A1 in the name of WIEDERRECHT discloses a gear of this type. EP Patent Application No. 1 983 389 A1 in the name of ETA SA presents an escapement mechanism wherein a balance roller has slots in proximity to impulse pallets arranged for cooperating with escapement wheels. U.S. Pat. No. 443,363 A in the name of HANSEN discloses an escapement mechanism including resilient damping means. WO Patent Application No. 2010/063393 A1 in the name of ROLLS ROYCE PLC discloses another toothing with teeth made flexible by the presence of slots connected to chambers.
In these embodiments, the travel, inherent in the flexibility of the arms, evaluated at the teeth is on the order of several hundredths or several tenths of a millimeter, which may prove too much in some mechanisms.